Oils and fats containing diacylglycerol in high concentrations are known to have physiological effects such as being less accumulative in the body (see Patent Document 1), and are widely used as edible oil. In regard to the processes for producing diacylglycerol, there are known processes involving an esterification reaction based on a chemical method or an enzymatic method, using fatty acids and glycerin as the raw materials (see Patent Document 2), a process of performing glycerolysis based on a chemical method or an enzymatic method, using oils and fats and glycerin as the raw materials, and the like (see Patent Documents 3 and 4).
Among the above-described processes for production, in one step in the process involving glycerolysis using oils and fats and glycerin as the raw materials, the reaction is completed, whereas in the process involving an esterification reaction using fatty acids and glycerin as the raw materials, above all, the fatty acids used as a raw material require a process of hydrolyzing oils and fats. In this case, since the hydrolysis reaction of oils and fats is usually carried out under high temperature and high pressure conditions, coloration may occur in some cases, depending on the conditions. Furthermore, in order to increase the purity of diacylglycerol in the reaction product, it is preferable to enhance the concentration of the raw material fatty acids. For that reason, it may become necessary to perform a distillation treatment after the hydrolysis of oils and fats (see Patent Document 5).
On the other hand, there are cases where, if a distillation treatment is performed after hydrolysis of oils and fats, the yield is decreased, or useful components present in plant oils, such as plant sterols or antioxidative components, are lost. Therefore, there has also been suggested a process in which the hydrolysate obtained after the hydrolysis of oils and fats is not distilled, but glycerin is added thereto, and an esterification reaction is performed (see Patent Document 6).
Moreover, in the process for producing diacylglycerol, a decoloration treatment is carried out, typically in the final stage, by using an adsorbent such as activated clay (see Patent Document 7).    [Patent Document 1] JP-A-10-176181    [Patent Document 2] JP-A-01-71495    [Patent Document 3] WO 03/29392    [Patent Document 4] JP-A-63-133992    [Patent Document 5] JP-A-2007-503524    [Patent Document 6] JP-A-11-123097    [Patent Document 7] JP-A-04-261497